I totally agree David, and I think Black, Brown and Beige is both representative of Duke speaking with actions and his work, and its reception (and that of Jump for Joy) perhaps explains why this was not done as frequently as he may have earlier envisioned he would practice showing his political mind.
I agree with Jim that he didn't have to make outright spoken political statements (although he did read all those Treasury Department blurbs in that series, but really I hardly consider that his real voice and thoughts). He did convey a lot of belief in the validity and potency of his race's place in American history and culture through his musical work and his bearing and deeds.